Method of making microwave tubes



S R mW 0E B m0 2 R v// ma N I A u o h v v H. 76 2 8 R 2 E 4 /B u A w\ w 3 G n 2 w w H A w W 2 W. VAN B. ROBERTS Filed June 27, 1946 METHOD OF MAKING MICROWAVE TUBES I I l/ June 27, 1950 FIG. I

A TTORNE Y Patented June 27, 1950 UNITED ES PATENT OFFICE METHOD OF MAKING MICROWAVE TUBES Walter van B3 Roberts, Silver Spring, Md., assignor to the United States of America: as representedby the Secretary ofathe Navy Application June 27, 1946, ,Serial No. 679,595

This invention relates to electric discharge devices and more particularly toan improved method of adjusting vacuum tubeelectro'des;

For microwave tubes it isdesirable to employ ring seals and close spacing of electrodes, together with electrode shapes that form a con tinuous part of the resonantline or cavity tank circuits cooperating with the electrodes. However, when ring seals and such electrodes have been used it has been found-:difiicult to obtain accurate control of the spacings.

It is therefore an object of my invention to make final adjustment of spacings in accordance with a continuous indication of' interelectrode capacity.

In the attainment of the foregoing object it is an important feature of my invention to make use of the interelectrode capacity of 'the electrodes as an indicator of spacing during the actual as sembly of the tube.

The phases of'this invention which I desire' to protect herein are particularly pointed out in the appended claim. The invention itself together with further obj ects andiadvantages thereof can best be understood by reference to the following descriptiontakew in conjunction with the accompanying drawings'of which" Fig. 1 is a cross-section view of a microwave-vacuum tube of the type to which this invention applies; Fig. 2 is a cross-section view showing the component parts of the tube of Fig. 1; Fig. 3 is a sectional view of a tube mountedin-theadjusting device; Fig. 4 is a schematic View ofithe' upper end! of the upper shaft of Fig. 3;- and. Fig. 5 illustrates a simple triode oscillator.

Referring particularly to Fig. 2, there are shown the three sections 5, 5 and 1 which when properly joined together form the tube ID of Fig. 1. This tube is seen as having electrodes adapted to external continuation to form resonant cavities and is well suited to external cooling of the anode.

These sections are each composed of an electrode with glass ring seals. Section 1 with cathode li also has a glass bead or two heads with the heater wires sealed in and an evacuating tip (not shown). Said cathode l1 has sufficient perforations or slits in the thimble-like cathode to permit evacuation from inside the cathode thimble.

For proper operation of this method of adjustment the sections 5, 6 and 1 when they are joined together to form said finished microwave tube II], the interelectrode spacing should be made greater than that ultimately desired. In joining the sections together to form the tube l0, they 2 are mounted in any suitable apparatus such as a lathe.

When a lathe is used to obtain the final adjustment of parts, the machine is employed as schematically shown by Figs. 3'and 4. A shaft Isis adapted to be attached to the headstock of a lathe, not shown, and carries a chuck l2. A shaft M is also adapted to be supported by the tailstock of the same lathe, not shown. To shaft M is. secured a container 21 suitably formed from insulating material. An electrically conducting extension I4 is attached to the container 2| anda pluralityof spring fingers ll secured to the extension I4. The chuck i2 and shaft I3 are groundedelectrically as schematically shown in Fig. 3. The electrode being not adjusted, such as I! in Fig. 3, is likewise grounded by a ground clip 20. To-obtain accuracy of results, the metal elements of the'tube are accurately machined or otherwise made up so as to insure theplane of the electrode when mounted in the chuck.- l2 being perpendicular to the shaft l3 and accurately centered.

Asshown in- Fig; 4, which fits immediately above-Fig.-: 3, thezoscillator of Fig. 5 whose tuned circuit utilizes the interelectrodecapacity of the electrodes being adjusted-as the frequencyxdetermining element.

Fi 5 illustrates a form of a suitableself-con tainedoscillator" for enclosure in container 2|; The ends of the inductance 24=aare connected by leads extending through the container 2!- to points 28 and as on the shafts l4 and. 14, re-- spectively. It is. a simple triode oscillator. comprising a suitable triode 22, power supplies 23 and El, filament chokes 25 and 25, grid biasing network and an appropriate inductance 24. The necessary capacitance for this oscillator circuit is the interelectrode capacity of the tube electrodes being adjusted which, in the case of those being adjusted in Fig. :3, are electrodes 15 and IS. The capacitance of these electrodes appears across the inductance 24 as schematically shown by the dotted line of Fig. 5, with the upper and lower plates l5 and i6, representing tube electrodes I5 and i6, respectively.

Any known type of oscillator may be used, the only requirement being that the electrodes of the tube under adjustment be connected to the oscillator so that their interelectrode capacity affects its frequency. Also in addition to this general method, it would be possible to use a separate oscillator and to couple this loosely to a second circuit comprising an inductance and I; the interelectrode capacity of the tube being assembled.

As the oscillator frequency is varied, a change in oscillator plate current will be observed as its frequency passes through resonance with said second circuit. The electrode spacings are adjusted until the frequency at which the change of plate current occurs has the certain desired value.

Final adjustment of the interelectrode spacing is to be made as shown in Fig. 3. For instance, the grid-to-anode spacing is adjusted as follows: a. chuck l2 on the lower shaft 13 grips the grid IS. The anode disc I is gripped by the spring fingers i l which tend to center said anode l5 and also tends to force the anode to be parallel to the grid I6. This whole arrangement is then mounted in a lathe (not shown), said lathe containing the customary means to provide accurate axially controlled movement of either shaft I 3 or 1:4. The whole arrangement is now rotated while a gas flame 30 is applied to the desired areas to soften the glass envelope in a ring between the anode !5 and the grid 16. As the glass softens, the spring fingers I I succeed in what they had only been tending to do and move the anode into exact alignment. The grid-anode spacing is then altered by moving the lathe controls until the oscillator within the insulated container 2| reaches a predetermined frequency, as is evident by its producing a beat frequency with an oscillating receiver. The gas flame 30 is then removed and the proper spacing of the electrodes is maintained by the shafts l3 and 14' while the glass hardens.

The adjustment of the grid-anode spacing having been completed, the tube is reversed and the grid-cathode spacing is similarly adjusted.

Any further shrinkage after the glass hardens can be allowed for by adjusting to a slightly wider spacing than desired in the final product. The amount of allowance necessary will be evident from the behavior of the first few tubes so adjusted.

As an alternative method, the sections 5, 6, 1 may be joined in the lathe. Thus, the spacing would be adjusted and the sealing made all in one operation. In this method the grid section 6 would first be sealed to one of the other sections, then turned over and sealed to the remaining one, each sealing being accompanied by spacing adjustment.

The predetermined frequency is arrived at as follows: a properly spaced similar pair or set of test electrodes (without seals) is put in the lathe.

The oscillator is turned on and the receiver adjusted to zero beat. Then when the electrodes under adjustment are at the same spacing, the oscillator will be heard on the receiver. The same non-visual process determines the setting of the receiver for adjusting grid-cathode spac- For extremely close adjustment it may be preferable to avoid vibration by holding the shafts I3 and I4 stationary and playing the gas flame from all sides, or rotating the flame.

While the invention is herein described by reference to particular embodiments thereof, it will be understood that numerous modifications may be made without actually departing from the true spirit and scope of the invention.

I claim:

The method of making a microwave tube having closely spaced tube electrodes ring-sealed in a tube envelope; said method comprising re-spacing said tube electrodes within said envelope after said tube is finished, by adjusting to a properly spaced set of test electrodes; said methodincluding the following steps: forming said tube so that said tube electrodes are spaced apart at a distance greater than that ultimately desired; maintaining a continuous non-visual indication of the interelectrode capacity of tube electrodes by means of an oscillator and a receiver circuit; using said capacity as the capacitance of said oscillator so that said capacity affects the frequency of said oscillator; holding a properly spaced set of un-sealed tube test electrodes in operating connection with said circuit; thereafter adjusting said receiver to zero beat; applying heat to soften a portion of said tube adjacent said tube electrodes; moving said tube electrodes within said softened portion until they attain a re-spaced position at which said oscillator is heard on said receiver; removing said heat from said portion; and retaining said tube electrodes in said re-spaced position until said portion has re-hardened.

WALTER VAN B. ROBERTS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,374,546 Laico Apr. 24, 1945 2,402,119 Beggs June 18, 1946 2,428,610 Beggs Oct. 7, 1947 2,452,652 Hansen Nov. 2, 19 8 

